This invention relates to a torque transmission device capable of intermittently switching torque transmission between an input rotary member and an output rotary member to rotate and stop the output rotary member at a specified rotational position.
In copying machines in which document images are copied on copy sheets, it has been known to be necessary to feed sheets intermittently at specified intervals when a variety of processings are applied to the sheets being transported. Feed rollers have been generally used to feed the sheets intermittently. A pair of feed rollers are arranged opposed to each other. Sheets inserted manually or transported by another feeding means from an upstream side are introduced to a nip between the roller pair and are fed to a downstream side one by one, and a desired processing is applied to the sheets at the downstream side. In this case, in order to feed the sheets by means of the feed rollers reliably, the feed rollers are caused to stop at specified rotational positions, and the sheet is inserted into the nip between the pair of feed rollers while rotation of the feed rollers is suspended. After the sheet is completely inserted into the nip, the feed rollers are drivingly rotated by means of a manual operation or upon automatically detecting the insertion of the sheet, so that the sheet can be fed to the downstream side reliably. Since the feed rollers are rotated and stopped at the specified positions alternately in this way, there is normally employed a spring clutch structure for transmitting on and off a torque to a rotary shaft of the feed rollers.
FIGS. 6A and 6B show a construction of an exemplary spring clutch. FIG. 6A is an exploded front view showing a mounting relationship of basic components of the spring clutch including a helical spring 100, a coupler 120 fixedly attached to an input shaft (driving side), a coupler 110 fixedly attached to an output shaft (feed roller side), and a collar 130. FIG. 6B is a side view of the coupler 110 when viewed from the right side.
The helical spring 100 has a specified inside diameter in a free state (i.e. in a state where no force is acting on the helical spring 100), and has an output end portion 101 and an input end portion 102 bent in axial directions thereof so as to serve as engaging portions respectively. Normally, the helical spring 100 is fabricated such that the phase of the output end portion 101 coincides with that of the input end portion 102 before they are placed on respective outer circumferential surfaces of the couplers 110 and 120. The couplers 110, 120 are designed such that the outside diameters thereof are at least slightly larger than the inside diameter of the helical spring 100. The helical spring 100 has one side portion thereof pressingly fitted on an outer circumferential surface of the coupler 110 and has the other side portion pressingly fitted on an outer circumferential surface of the coupler 120. On an output end of the coupler 110 and an input end of the collar 130 are provided flanges having a large diameter. The collar 130 is rotatable on the coupler 120. In the flange of the coupler 110 is formed a groove 111 in which the output end portion 101 of the helical spring 100 is fitted. Likewise, in the flange of the collar 130 is formed a hole (or groove) 131 in which the input end portion 102 of the helical spring 100 is fitted. By fitting the output and input end portions 101. 102 in the groove 111 and the hole 131 respectively, the collar 130 and the helical spring 100 are prevented from idly rotating. The coupler 110 is formed with a D-shaped hollow having a fitting surface 112 as shown in FIG. 6B. To the fitting surface 112 is fitted an unillustrated rotary shaft of the feed roller (a mating portion of the rotary shaft has at least a similar D-shaped cross-section), thus enabling the coupler 110 and the unillustrated rotary shaft of the feed roller to rotate integrally. Indicated at 132 is a projection formed at a specified position on the flange of the collar 130. When the projection 132 is in a specified rotational position, the spring clutch is caused to be disengaged. More specifically, the projection 132 comes into contact with an unillustrated stopping member, and a force acts in a direction opposite to a winding direction of the helical spring 100. As a result, the helical spring 100 is loosened radially and only the coupler 120 rotates with sliding on the inside surface of the spring 100. Consequently, the clutch is disengaged and the transmission of the torque from the coupler 120 to the coupler 110 is interrupted. In this way, the feed roller is controllably caused to rotate and stop at the specified rotational position.
As described above, the feed roller can be stopped at the specified rotational position when an angular position of the collar 130 whose rotation is regulated by the combination of the projection 132 and the stopping member is held in specific corresponding relation to the phase of the feed roller mounted on the rotary shaft fitted to the fitting surface 112 of the coupler 110. Thereby, the sheets can be inserted into the nip between the stationary feed roller pairs reliably.
The phase relationship between the input end portion 102 of the helical spring 100 and the fitting surface 112 of the coupler 110 is determined by the phase relationship between the input end portion 102 and output end portion 101 of the helical spring 100. However, the phase relationship between both end portions 101, 102 is not in a fixed relationship and is liable to change with springs and couplers. Accordingly, the phase relationship between the input end portion 102 and the fitting surface 112 is not fixed. Consequently, it is difficult to control stopping of the rotary shaft fitted on the coupler 110 at a specified rotational position.
More specifically, the output and input end portions 101, 102 of the helical spring 100 have a specific phase relationship (for example, they are in the same phase in FIG. 6A) until the helical spring 100 is mounted on the couplers 110 and 120. However, since the outside diameters of the couplers 110, 120 are set slightly larger than the inside diameter of the helical spring 100, the diameter of the helical spring 100 is increased when the helical spring 100 is mounted on the couplers 110 and 120. Accordingly, the phase relationship between the output and input end portions 101, 102 changes with changes in the fitting or mating lengths of the helical spring 100 and the couplers 110 and 120. In FIG. 6A, for example, when the input end portion 102 is fitted in the hole 131, the collar 130 rotates, and the projection 132 consequently shifts. It should be noted that production of couplers and springs involve dimensional variations for various reasons. Accordingly, the phase relationship between the input end portion 102 and the output end portion 101 differs in individual products due to the dimensional variations. Thus, it will be impossible to assure a fixed phase relationship between the input end portion 102 and the fitting surface 112 of the coupler 110, and to then stop the output shaft or the feed roller at a specified rotational position.